Anti-abnormal-pressure/vacuum valve

ABSTRACT

An improved anti abnormal-pressure/vacuum valve has a sleeve-like valve provided with a projection at its front end projecting into an actuator-side port, and a pressure introducing tube in a spool valve slidable in the sleeve-like valve for introducing oil pressure into a valve pressing chamber at the rear of the sleeve-like valve has its front-end portion disposed inside a front-end surface of the spool valve. This converts a dynamically varying pressure in the actuator-side port into a statically varying pressure in the valve pressing chamber so as to prevent the sleeve-like valve from being accidentally separated from its valve seat when oil pressure in the actuator-side port varies dynamically.

FIELD OF THE INVENTION

The present invention relates to an anti abnormal-pressure/vacuum valveinstalled in a control valve provided in a hydraulic circuit for drivingan actuator employed in construction machines and the like.

DESCRIPTION OF THE PRIOR ART

A conventional control valve installed in a hydraulic circuit fordriving an actuator employed in machine has a construction, for examplesuch as that shown in FIG. 1, in which: a spool valve 4 is movablymounted in a valve body 1 of the control valve so as to permit/preventcommunication between a pump-side port 2 and an actuator-side port 3 inthe valve body 1, whereby pressure oil supplied from a hydraulic pump(not shown) to the pump-side port 2 of the valve body 1 is controlled soas to be appropriately supplied to the actuator (not shown) of themachine through the actuator-side port 3 of the valve body.

In the conventional control valve having the above construction, inorder to prevent excessive oil pressures or abnormal pressures frombeing produced in the hydraulic circuit when the actuator is overloaded,and also in order to prevent a possible vacuum from developing in theactuator due to a deficiency of pressure oil therein when the actuatoris moved by an external force, there is provided an antiabnormal-pressure/vacuum valve "A" for permitting/preventing thecommunication between the actuator-side port 3 and a reservoir-side port5 in the valve body 1 of the control valve, as shown in FIG. 1.

The anti abnormal-pressure/vacuum valve "A" provided in the conventionalcontrol valve has a construction, for example, such as that shown inFIG. 2.

In the construction of the conventional anti abnormal-pressure/vacuumvalve "A", as shown in FIG. 2, a sleeve-like valve 11 is slidablymounted in a sleeve-like case 10 in an insertion manner. In a front endportion of the valve 11 are formed: a first port 12; and a second port13. A spool valve 14 is slidably mounted in the sleeve-like valve 11 inan insertion manner so as to permit/prevent communication between thefirst port 12 and the second port 13 of the sleeve-like valve 11, whilepressed against a valve seat formed in a peripheral portion of the firstport 12 of the sleeve-like valve 11 under the influence of a resilientforce exerted by a compression spring 15 to prevent the communicationbetween the first port 12 and the second port 13. A pressure-introducingtube 16 is slidably mounted in the spool valve 14 in an insertion mannerto permit communication between the actuator-side port 3 of the valvebody 1 and a valve pressing chamber 17, so that the sleeve-like valve 11is pressed against a valve seat 1a under the influence of a pressure ofthe pressure oil supplied to the valve pressing chamber 17 from theactuator-side port 3 through a central port of the pressure-introducingtube 16. The valve seat 1a is formed in a peripheral portion of theactuator-side port 13 of the valve body 1.

In the conventional anti abnormal-pressure/vacuum valve "A" having theabove construction, when the valve "A" is subjected to excessivepressure or abnormal pressure at the actuator-side port 13, the spoolvalve 14 is moved rightward as viewed in FIG. 2 against the resilientforce exerted by the compression spring 15 under the influence of suchexcessive pressure or abnormal pressure to permit the communicationbetween the first port 12 and the second port 13, so that the pressureoil supplied to the actuator-side port 3 at such excessive pressure ofabnormal pressure flows out of the port 3 to the reservoir-side port 5,whereby the abnormal pressure is removed from the valve body 1 of thecontrol valve.

On the other hand, in the conventional anti abnormal-pressure/vacuumvalve "A" having the above construction, when the valve "A" is subjectedto a possible vacuum at the actuator-side port 13, a pressure in thevalve pressing chamber 17 reduces so that the sleeve-like valve 11 ismoved rightward as viewed in FIG. 2 under the influence of a rightwardforce acting on the sleeve-like valve 11. Such rightward force issubstantially a product of a predetermined area and a pressure of thepressure oil in the reservoir-side port 5, the predetermined area beinga difference in cross-sectional area between a bore of the sleeve-likecase 10 having an inner diameter d₁ and the actuator-side port 3 havingan inner diameter d₂. As a result of the above-described rightwardmotion of the sleeve-like valve 11, the sleeve-like valve 11 isseparated from the valve seat 1a of the valve body 1 to permitcommunication between the actuator-side port 3 and the reservoir-sideport 5, so that the pressure oil in the reservoir-side port 5 isintroduced into the actuator-side port 3 to prevent a possible vacuumfrom developing in the actuator-side port 3 of the valve body 1 of thecontrol valve.

However, since the conventional anti abnormal-pressure/vacuum valve "A"employed in the control valve has the above construction, thepressure-introducing tube 16 extends leftward as viewed in FIG. 2 toenter the actuator-side port 3. Consequently, when the pressure in thepressure oil in the actuator-side port 3 varies dynamically, thepressure in the pressure oil in the valve pressing chamber 17 alsodynamically varies to permit the sleeve-like valve 11 to accidentallyseparate from the valve seat 1a of the valve body 1 even when no vacuumdevelops in the actuator-side port 3. Therefore, as is clear from theabove description, in the conventional anti abnormal-pressure/vacuumvalve "A", there is a fear that the pressure oil supplied from thepump-side port 2 to the actuator-side port 3 is drained back into thereservoir-side port 5 by accident.

Incidentally, as an example of dynamic variation in pressure of thepressure oil in the actuator-side port 3 of the valve body 1 may becited the fact that: as shown in FIG. 1, when the spool valve 4 isgradually moved rightward to have its concave portion 4a slightly enterthe actuator-side port 3, jets of the pressure oil supplied from thepump-side port 2 are spouted into the actuator-side port 3 to cause thepressure oil in the actuator-side port 3 to dynamically vary.

SUMMARY OF THE INVENTION

Under such circumstances, the present invention was made. Therefore, itis an object of the present invention to provide an antiabnormal-pressure/vacuum valve installed in a control valve provided ina hydraulic circuit for driving an actuator employed in constructionmachines and the like, which anti abnormal-pressure/vacuum valve of thepresent invention eliminates dynamic variations in pressure of thepressure oil in the hydraulic circuit to permit the pressure oil to varystatically in the hydraulic circuit so that the thus statically varyingpressure oil is introduced into the valve pressing chamber 17 oppositelydisposed from the actuator-side port 3 to prevent pressure oil havingsupplied to the actuator-side port 3 from being drained back into thereservoir-side port 5 by accident.

In accordance with a first aspect of the present invention, the aboveobject of the present invention is accomplished by providing:

In an anti abnormal-pressure/vacuum valve comprising: a first and asecond port both of which are formed on a front-end side of asleeve-like valve for permitting/preventing communication between anactuator-side port and a reservoir-side port both of which are formed ina valve body of a control valve provided in a hydraulic circuit fordriving an actuator employed in construction machines and the like, thefirst and the second port being in communication with the actuator-sideport and the reservoir-side port, respectively; a spool valve slidablymounted in the sleeve-like valve, for permitting/preventingcommunication between the first port and the second port, thecommunication between the first port and the second port being preventedby a resilient force exerted by a compression spring and being permittedwhen the resilient force exerted by the compression spring is overcomeby a pressure of the pressure oil in the actuator-side port; and apressure introducing tube slidably mounted in the spool valve, forintroducing the pressure of the pressure oil supplied to theactuator-side port into a valve pressing chamber so as to press thesleeve-like valve against a valve seat formed in the valve body of thecontrol valve; whereby the sleeve-like valve is separated from the valveseat when the pressure oil in the actuator-side port is smaller inpressure than that in the reservoir-side port,

the improvement wherein:

the sleeve-like valve is provided with a sleeve-like projection at itsfront end, which projection projects into the actuator-side port; andthe pressure introducing tube has its front-end portion disposed insidea front-end surface of the spool valve.

In the anti abnormal-pressure/vacuum valve of the present inventionhaving the above construction, it is possible for the sleeve-likeprojection of the sleeve-like valve to eliminate a fear that thepressure of the pressure oil in the actuator-side port variesdynamically, so that the statically varying pressure of the pressure oilis introduced into the valve pressing chamber through the pressureintroducing tube. Consequently, in the anti abnormal-pressure/vacuumvalve of the present invention, there is no fear that the sleeve-likevalve is accidentally separated from the valve seat even when thepressure of the pressure oil in the actuator-side port tends to varydynamically.

As a result, it is possible for the anti abnormal-pressure/vacuum valveof the present invention to prevent the pressure oil in theactuator-side port from being accidentally drained back into thereservoir-side port, the pressure oil being supplied to theactuator-side port from the pump-side port.

The above object, additional objects, additional embodiments andadvantages of the present invention will be clarified to those skilledin the art hereinbelow with reference to the following description andthe accompanying drawings illustrating preferred embodiments of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an essential part of theconventional control valve provided in the hydraulic circuit for drivingthe actuator employed in the construction machines and the like;

FIG. 2 is a cross-sectional view of the conventional antiabnormal-pressure/vacuum valve; and

FIG. 3 is a cross-sectional view of an anti abnormal-pressure/vacuumvalve of a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 3, there is shown an anti abnormal-pressure/vacuum valve of apreferred embodiment of the present invention, which valve is mounted inthe valve body 1 of the control valve shown in FIG. 2.

As is clear from FIGS. 1 to 3, the conventional antiabnormal-pressure/vacuum valve shown in FIG. 2 is partially improved inaccordance with the present invention to become the preferred embodimentof the present invention shown in FIG. 3. As described above, both theanti abnormal-pressure/vacuum valve of the prior art shown in FIG. 2 andthat of the prevent invention shown in FIG. 3 are basically the same instructure, and, therefore the description of the basic structure of theanti abnormal-pressure/vacuum of the present invention shown in FIG. 3is omitted by representing the like elements by like reference numeralsto avoid redundancy in description hereinbelow.

As shown in FIG. 3, a sleeve-like valve 11 is provided with asleeve-like projection 11a in its front end, which projection 11a isintegrally formed with the sleeve-like valve 11 to project into theactuator-side port 3 formed in the valve body 1 of the control valve. Onthe other hand, a front end 16a of a pressure introducing tube 16 isdisposed inside a front-end surface 14a of the spool valve 14.

Since the anti abnormal-pressure/vacuum valve of the present inventionhas the above construction, when the pressure of the pressure oil in theactuator-side port 3 varies dynamically, such dynamically varyingpressure of the pressure oil in the actuator-side port 3 exerts upon thesleeve-like projection 11a of the sleeve-like valve 11 so as to beconverted into a statically varying pressure which is introduced intothe valve pressing chamber 17 through the pressure introducing tube 16,the valve pressing chamber 17 being oppositely disposed from theactuator-side port 3. Consequently, it is possible for the antiabnormal-pressure/vacuum valve of the present invention to prevent thesleeve-like valve 11 from being accidentally separated from the valveseat 1a even when the pressure of the pressure oil in the actuator-sideport 3 varies dynamically, the valve seat 1a being formed in the valvebody 1 of the control valve.

I claim:
 1. In an anti abnormal-pressure/vacuum valve comprising: afirst and a second port both of which are formed on a front-end side ofa sleeve-like valve for permitting/preventing communication between anactuator-side port and a reservoir-side port both of which are formed ina valve body of a control valve provided in a hydraulic circuit fordriving an actuator employed in construction machines and the like, saidfirst and said second port being in communication with saidactuator-side port and said reservoir-side port, respectively; a spoolvalve slidably mounted in said sleeve-like valve, forpermitting/preventing communication between said first port and saidsecond port, said communication between said first port and said secondport being prevented by a resilient force exerted by a compressionspring and being permitted when the resilient force exerted by saidcompression spring is overcome by a pressure of the pressure oil in saidactuator-side port; and a pressure introducing tube slidably mounted insaid spool valve, for introducing the pressure of the pressure oilsupplied to said actuator-side port into a valve pressing chamber so asto press said sleeve-like valve against a valve seat formed in saidvalve body of the control valve; whereby said sleeve-like valve isseparated from said valve seat when the pressure oil in saidactuator-side port is smaller in pressure than that in saidreservoir-side port,the improvement wherein: said sleeve-like valve isprovided with a sleeve-like projection at its front end, whichprojection projects into said actuator-side port; and said pressureintroducing tube has its front-end portion disposed inside a front-endsurface of said spool valve.